Triglycerides represent the major form of energy stored in eukaryotes. Disorders or imbalances in triglyceride metabolism are implicated in the pathogenesis of and increased risk for obesity, insulin resistance syndrome and type II diabetes, nonalcoholic fatty liver disease and coronary heart disease (see, Lewis, et al, Endocrine Reviews (2002) 23:201 and Malloy and Kane, Adv. Intern. Med. (2001) 47:11 1). Additionally, hypertriglyceridemia is often an adverse consequence of cancer therapy (see, Bast, et al. Cancer Medicament, 5th Ed., (2000) B.C. Decker, Hamilton, Ontario, Calif.).
A key enzyme in the synthesis of triglycerides is acyl CoA:diacylglycerol acyltransferase, or DGAT. DGAT is a microsomal enzyme that is widely expressed in mammalian tissues and that catalyzes the joining of 1,2-diacylglycerol (DAG) and fatty acyl CoA to form triglycerides (TG) at the endoplasmic reticulum (reviewed in Chen and Farese, Trends Cardiovasc. Med. (2000) 10: 188 and Farese, et al, Curr. Opin. Lipidol. (2000) 11:229). It was originally thought that DGAT uniquely controlled the catalysis of the final step of acylation of diacylglycerol to triglyceride in the two major pathways for triglyceride synthesis, the glycerol phosphate and monoacylglycerol pathways. Because triglycerides are considered essential for survival, and their synthesis was thought to occur through a single mechanism, inhibition of triglyceride synthesis through inhibiting the activity of DGAT has been largely unexplored.
Genes encoding mouse DGAT1 and the related human homologs ARGP1 (human DGAT1) and ARGP2 (human ACAT2) now have been cloned and characterized (Cases, et al, Pro.c Nat.l Acad. Sci. (1998) 95:13018; Oelkers, et al, J. Biol. Chem. (1998) 273:26765). The gene for mouse DGAT1 has been used to create DGAT knock-out mice to better elucidate the function of the DGAT gene.
Unexpectedly, mice unable to express a functional DGAT1 enzyme (Dgat1−/− mice) are viable and still able to synthesize triglycerides, indicating that multiple catalytic mechanisms contribute to triglyceride synthesis (Smith, et al, Nature Genetics (2000) 25:87). Other enzymes that catalyze triglyceride synthesis, for example, DGAT2 and diacylglycerol transacylase, also have been identified (Cases, et al, J. Biol. Chem. (2001) 276:38870). Gene knockout studies in mice have revealed that DGAT2 plays a fundamental role in mammalian triglyceride synthesis and is required for survival. DGAT2 deficient mice are lipopenic and die soon after birth, apparently from profound reductions in substrates for energy metabolism and from impaired permeability barrier function in the skin. (Farese, et al., J. Biol. Chem. (2004) 279: 11767).
Significantly, Dgat1−/− mice are resistant to diet-induced obesity and remain lean. Even when fed a high fat diet (21% fat) Dgat1−/− mice maintain weights comparable to mice fed a regular diet (4% fat) and have lower total body triglyceride levels. The obesity resistance in Dgat1−/− mice is not due to decreased caloric intake, but the result of increased energy expenditure and decreased resistance to insulin and leptin (Smith, et al, Nature Genetics (2000) 25:87; Chen and Farese, Trends Cardiovasc. Med. (2000) 10: 188; and Chen, et al, J. Clin. Invest. (2002) 109:1049). Additionally, Dgat1−/− mice have reduced rates of triglyceride absorption (Buhman, et al, J. Biol. Chem. (2002) 277:25474). In addition to improved triglyceride metabolism, Dgat1−/− mice also have improved glucose metabolism, with lower glucose and insulin levels following a glucose load, in comparison to wild-type mice (Chen and Farese, Trends Cardiovasc. Med. (2000) 10: 188).
The finding that multiple enzymes contribute to catalyzing the synthesis of triglyceride from diacylglycerol is significant, because it presents the opportunity to modulate one catalytic mechanism of this biochemical reaction to achieve therapeutic results in an individual with minimal adverse side effects. Compounds that inhibit the conversion of diacylglycerol to triglyceride, for instance by specifically inhibiting the activity of DGAT1, will find use in lowering corporeal concentrations and absorption of triglycerides to therapeutically counteract the pathogenic effects caused by abnormal metabolism of triglycerides in obesity, insulin resistance syndrome and overt type II diabetes, congestive heart failure and atherosclerosis, and as a consequence of cancer therapy.
Because of the ever increasing prevalence of obesity, type II diabetes, heart disease and cancer in societies throughout the world, there is a pressing need in developing new therapies to effectively treat and prevent these diseases. Therefore there is an interest in developing compounds that can potently and specifically inhibit the catalytic activity of DGAT, in particular DGAT1.
We have now unexpectedly found that novel compounds exhibiting DGAT inhibitory activity, in particular DGAT1 inhibitory activity, and these compounds can therefore be used to prevent or treat a disease associated with or mediated by DGAT, such as for example obesity, type II diabetes, heart disease and cancer. The compounds of the invention differ from the prior art compounds in structure, in their pharmacological activity, pharmacological potency, and/or pharmacological profile.
We have also unexpectedly found that DGAT inhibitors, including the DGAT inhibitors of the present invention, can be used to elevate the levels of one or more satiety hormones, in particular glucagon-like-peptide-1 (GLP-1) and therefore DGAT inhibitors, in particular DGAT1 inhibitors, can also be used to prevent or treat a disease which can benefit from elevated levels of a satiety hormone, in particular GLP-1. Glucagon-like peptide 1 (GLP-1) is an intestinal hormone which generally stimulates insulin secretion during hyperglycemia, suppresses glucagon secretion, stimulates (pro) insulin biosynthesis and decelerates gastric emptying and acid secretion. GLP-1 is secreted from L cells in the small and large bowel following the ingestion of fat and proteins. GLP-1 has been suggested, among other indications, as a possible therapeutic agent for the management of type II non-insulin-dependent diabetes mellitus as well as related metabolic disorders, such as obesity.
The present novel compounds make it possible to treat a disease which can benefit from elevated levels of GLP-1 with small molecules (compared to large molecules such as proteins or protein-like compounds, e.g. GLP-1 analogues).
The peroxisome proliferator-activated receptors (PPAR) belong to the steroid hormone nuclear receptor superfamily of ligand-activated transcription factors that mediate the specific effects of small lipophilic compounds, such as steroids, retinoids and fatty acids, on DNA transcription. They play an important role in the regulation of lipid metabolism, in the regulation of energy homeostasis, inflammation, artherosclerosis and glucose control. Three subtypes are identified so far, namely PPAR-α, PPAR-β/δ and PPAR-γ. The three isoforms exhibit different tissue distribution as well as different ligand specificities.
PPAR-α plays a crucial role in the intracellular lipid metabolism. The PPAR-α subtype is mainly expressed in tissues with elevated mitochondrial and peroxisomal fatty acid β-oxidation rates, that efficiently harvest energy from lipids, including liver, skeletal muscle, heart muscle, proximal tubular epithelial cells of the kidney, and brown fat (brown adipose tissue). PPAR-α is also present in cells of the arterial wall, in monocytes/macrophages, smooth muscle cells, endothelial cells, in hepatocytes, and in cardiac myocytes.
Saturated and unsaturated fatty acids are found to be the primary natural PPAR-α ligands. In general, PPAR-α can be activated by a heterogeneous group of compounds, which include natural and synthetic agonists, such as eicosanoids, leukotriene β4, carbaprostacyclin, nonsteroidal anti-inflammatory drugs, pirinixic acid (WY-14643; PPAR-α/γ agonist), phthalate ester plasticizers, pterostilbene, fibrates or active metabolites thereof, α-substituted phenyl-propanoic acid derivatives and isoxazolyl-serine-based compounds. Finally, PPAR-α is induced by glucocorticoids in response to stress and follows a diurnal rhythm.
Fibrates or active metabolites thereof such as fibric acid derivatives, are PPAR-α agonists, and have been used to treat dyslipidemia for several decades because of their triglyceride lowering and high-density lipoprotein (HDL) cholesterol elevating effects. Fibric acid derivatives lower the levels of triglyceride-rich lipoproteins, such as very low-density lipoproteins (VLDL), raise HDL levels, and have variable effect on low-density lipoproteins (LDL) levels. The effects on VLDL levels appear to result primarily from an increase in lipoprotein lipase activity, especially in muscle. This leads to enhanced hydrolysis of VLDL triglyceride content and an enhanced VLDL catabolism. Fibric acid agents also may alter the composition of the VLDL, for example, by decreasing hepatic production of apoC-III, an inhibitor of lipoprotein lipase activity. These compounds are also reported to decrease hepatic VLDL triglyceride synthesis, possibly by inhibiting fatty acid synthesis and by promoting fatty acid oxidation. In addition, they have been documented to be beneficial in the prevention of ischemic heart disease in individuals with dyslipidemia and they can also modestly decrease elevated fibrinogen and PAI-1 levels. Well-known examples of fibrates are fenofibrate (fenofibric acid as active metabolite), ABT-335 (which is the choline salt of fenofibric acid), bezafibrate, clofibrate, ciprofibrate, etofibrate, pirifibrate, beclofibrate and gemfibrozil (PPAR-α modulator).
Because of the ever increasing prevalence of obesity, type II diabetes, heart disease and cancer in societies throughout the world, there is a pressing need in developing new therapies to effectively treat and prevent these diseases.
We have now unexpectedly found that the combination of a compound showing DGAT inhibitory activity, in particular DGAT1 inhibitory activity, with a PPAR agonist, in particular a PPAR-α agonist, may exhibit an increased and/or accelerated effect on weight loss, compared to the effect of the DGAT inhibitor or the PPAR agonist each separately, and additional can decrease food intake. The combinations of the present invention may show synergy compared to administration of the composing ingredients alone.